Liquid crystals mesomorphic behavior

Depending on the R group, this reaction could lead to the formation of gold(I) isocyanide complexes that behave as liquid crystals. Thus, complexes [Au(C6F5) (C = N(QH4)OCioH2i-p)] and [Au(QF5)(C = N(QH4)OCnH2n + rP)] [64] where n = 4, 6, 8, 10 and 12 show this behavior. All of these complexes are mesomorphic and behave as liquid crystals showing a nematic (N) phase when the isocyanide has a... 

Another approach to get new liquid crystals is the lateral fluorination of the stilbazole ligands,337 which is a common and highly effective tool to exert control over mesomorphism, crystal phase stability, and physical properties. Other modifications include the use of more alkoxy substituents and other alkyl sulfate anions.338-344 Ionic silver amino complexes also display liquid crystalline behavior at rather low temperatures they are of the form [Ag(NH2 -CJl +OJX (X = N03, n = 6,8,10,12,14 X = BF4, = 8,10,12,14).345... 

Mesogen a substance that shows liquid crystal behavior (exhibits mesomorphism). Isotropic state conventional liquid state. 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

Having found that gold triflates were mesomorphic, we returned to silver and decided to look at other anions. In so doing, we made complexes of silver trifiate and nitrate, each of which exhibited similar patterns of liquid-crystal behavior namely, the formation of Sc and Sa phases at rather elevated temperatures (the phase diagram for the nitrates is reproduced in Fig. 40) (54). While neither of these systems showed a cubic phase, we did find a nematic phase in the triflates. 

Having synthesized a number of complexes of monoalkoxystilbazoles, we explored the effect of using various poly(alkoxy)stilbazoles, given the interesting mesomorphism found in polycatenar mesogens (Section VI,A,3). This work is discussed in detail elsewhere 24). Here, we give an overview of the work to enable the reader to see the overall pattern of liquid-crystal behavior and the issues that arise. 

In this chapter we have described the mesomorphic behavior and ionic conductivities of ionic liquid-based liquid crystalline materials. These ion-active anisotropic materials have great potentials for applications not only as electrolytes that anisotropically transport ions at the nanometer scale but also as ordered solvents for reactions. Ionic liquid crystals have also been studied for uses as diverse as nonliner optoelectronic materials [61, 62], photoluminescent materials [78], structuredirecting reagents for mesoporous materials [79, 80] and ordered solvents for organic reactions [47, 81]. Approaches to self-organization of ionic liquids may open a new avenue in the field of material science and supramolecular chemistry. 

Lipids constitute a diverse and important group of biomolecules. Most lipids can behave as lyotropic liquid crystals. In the presence of water, they self-assemble in a variety of phases with different stmcture and geometry. The lipid polymorphic and mesomorphic behavior, i.e., their ability to form various ordered, crystalline, gel, or liquid-crystalline phases as a function of water content, temperature, and composition, is one of the most intriguing features of lipid-water systems. The mutual transformations between these phases and their physiologic implications are the subject of this article. 

Interesting liquid crystal properties resulted from the Schiff-base derivatives 11 [18]. All compounds exhibited mesomorphic behavior (Fig. 9-6). The first members of the series gave rise to enantiotropic nematic phases and the long chain derivatives exhibited enantiotropic smectic A phases. The intermediate chain length derivatives presented monotropic nematic or smectic A phases. 

Further studies by Nishiyama et al. [34-45] showed that when taken in isolation, only one of the aromatic units within a supermolecular system has a propensity to exhibit liquid crystal phases, then the supermolecular material itself could be mesomorphic, see Fig. 5. For example, for the top molecular structure, 5 [45], in Fig. 5, only the biphenyl unit at the center of the structure supports mesophase formation, whereas the benzoate units are too isolated from the biphenyl moiety in order to affect mesomorphic behavior. The second material, 6 [45] has terminal phenyl units, which are only connected by aliphatic chains to the benzoate units. Thus in this case, the material has four aromatic units out of six which are not in positions that can enhance mesophase formation. However, the second material has similar transition temperatures and phase sequences to the first, i.e., both materials exhibit an unidentified smectic phase and a synclinic ferroelectric smectic C phase. If the third material, 7 [38], is examined, it can be seen that the mesogenic unit at the center of the supermolecule is an azobenzene unit which is more strongly supportive of mesophase behavior than the simple biphenyl moiety. Thus the clearing point is higher for this material in comparison to the other two. The attachment of the terminal phenyl unit is by a methylene spacer of odd parity, and as a consequence the smectic C phase has an anticlinic structure rather than synclinic. 

Membrane lipids can exist in a number of intermediate states or mesophases more ordered than the liquid but less so than the crystalline solid [102, 131, 136]. Such materials are called liquid crystals and their multiple intermediate phase character is termed mesomorphism. There are at least four types of mesomorphic behavior lyotropic, thermotropic, barotropic and ionotropic. These refer to the expression of the disparate liquid crystal phases by manipulating solvent (lyotrope) content, temperature, pressure, and salt concentration, respectively. Most membrane lipids exhibit the four types of mesomorphism. 

Two homologs of 78a (M = Pt, X = Cl, = 4, 6) were investigated in the formation of LB fdms. "" It was found that better fdms were obtained with the homolog that was mesomorphic at room temperature (n = 6). In the absence of more data, it is difficult to know how strongly this is correlated with the ambient liquid-crystal behavior of the material, or whether it results from a much lower degree of amphipathy due to the shorter chains. For example, well-ordered LB films of Ir(l) stilbazoles (71, see Section X.11.2) have been formed where the mesophase of the complex is found above 85 °C. 

The acetylide complexes 90 were synthesized on Pt rather than on Pd, due to the lability of the latter metal that precluded isolation of such species other than Pt. These species were accessed as neutral analogs of related Ag(l) complexes in order to try to delineate the effect on the mesomorphism of the charge on the silver complexes and how this might relate to the stability of the cubic phase seen extensively in the silver complexes.The Pt-acetylide complexes turned out to be predominantly nematic in their phase behavior and the consequences in relation to cubic phase behavior were discussed. Curiously, however, the complexes did, in addition, show a SmC phase. It is almost universally true that liquid crystals bearing lateral chains show only nematic phases,and so this aspect of the behavior of Pt complexes still requires explanation. 

Liquid crystals are unique molecular materials because of their anisotropic nature and molecular dynamics [1-4]. Over the last three decades, these materials have been developed as advanced materials for electrooptical applications such as display devices. Liquid crystals also have close relationships to biomolecular systems [5]. Cell membranes form dynamic and anisotropic molecular states, which possess liquid-crystalline behavior. Recently, liquid-crystalline complexes of DNAs and liposomes have been considered as potential systems for gene therapy [6]. The design of liquid crystals by using a variety of structures and interactions may lead to wider applicability of mesomorphic materials. 

Double hydrogen bonding has been used for molecular recognition and organization [60]. Doubly H-bonded supramolecular liquid-crystalline complexes based on 2,6-bis(acylamino)pyridines show unique mesomorphic behavior. Complexes 21 exhibit monotropic crystal B phases [61, 62]. 

The combination of the stabilization effect by molecular orientation in liquid crystals, the geometry effect, and the relatively strong bonding energy of the carboxylic acid/pyridine interaction, leads to the formation of supramo-lecular liquid-crystalline materials which exhibit stable mesomorphic behavior. The stability and molecular orientation for H-bonded systems have been discussed theoretically [72-74]. 

Ordinarily a crystalline solid melts sharply at a single, well-defined temperature to produce a Uquid phase that is amorphous and isotropic. A different behavior is exhibited by a class of organic compounds known as liquid crystals. The oldest examples are cholesterol derivatives, e.g., cholesteryl benzoate. This substance, for instance, does not have a sharp transition to amorphous Uquid at 145.5°C, but changes to a cloudy liquid, which becomes clear and isotropic only at 178.5°C. This cloudy intermediate state that possesses an ordered stmcture with some resemblance to a crystaUine soUd, while still in the liquid state, is called a mesophase or mesomorphic phase from the Greek mesos, meaning in between or intermediate. 

Thermotropic Liquid Crystals. - Organic molecules, having aromatic rings or unsaturations thus producing elongated shapes, and also polymeric molecules often show thermotropic phase behavior. Mesomorphism comprises typically nematic, smectic A and B, and cholesteric thermotropic phases, but in several cases columnar, discotic and rod-disk self-assembly shapes of thermosensitive mesogens have been observed. 

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